1. Field of the Invention
This invention relates to a mechanism for transporting substrates. More particularly a transfer chamber is provided by which substrates may be transferred from one processing workstation system to an adjacent processing workstation system.
2. Brief Description of Related Developments
The processing of semiconductors often involves multiple process steps such as the deposit of a film on a substrate by chemical vapor deposition (CVD), the photo etching of the film, as well as heating, cooling and cleaning.
Such process operations may be performed under vacuum in specialized process chambers. Generally multiple process chambers are grouped in association with substrate handling mechanism to form a workstation system. Depending on the nature of each process, either batch processing of semiconductor substrates or individual substrate processing is used.
In batch processing, a cluster of processing chambers are arranged to form a workstation system. The processing chambers are positioned around a substrate transport chamber, constructed to be kept under a controlled atmosphere or vacuum. One or more load lock chambers are connected through slit valves to the transport chamber and act as a transfer station between ambient atmosphere and processing atmosphere.
A robotic transport mechanism, generally in the form of a robot is mounted within the transport chamber and operates to remove substrates from the load lock and deliver them to the selected process chambers. After processing, the substrates are picked up by the robot and transported to the next process chamber or to a load lock for removal from the transport chamber.
A system of this type is described in U.S. Pat. No. 5,882,413 and an example of a robotic transfer mechanism is shown in U.S. Pat. No. 5,647,724, each of which is assigned to an owner common to this application. The disclosures of these patents are incorporated herein by reference in their entirety.
It has been found that substrates up to 200 mm in diameter can be effectively processed with the cluster type workstation systems. However, there is a trend towards increasing diameters and the cluster systems become unduly large when processing substrates of 300 mm or more in diameter. In some circumstances, there is a need to provide a more compact process handling module, which is capable of being installed in a side by side relation within a small footprint of space. In addition there is a need for system modules which are more adaptable to the wide variety of process chambers and front end delivery transports. A system of this type is described in commonly owned Application for patent Ser. No. 09/897,202 filed Jul. 2, 2001. Such systems employ a front end loader which may be connected to the load locks of a pair of processing chambers situated side by side. A robot may be mounted within the front end loader to extract substrates for processing from cassettes. The robot may be mounted on a track to shuttle from one load lock to the other as shown in U.S. Pat. No. 6,002,840.
Regardless of the type of system (i.e. batch or individual processing) employed in a fabrication facility, (but generally more so in the case of batch processing) a substrate may be conventionally transported in cassettes from workstation systems to other workstation systems in a production sequence by automated material handling systems such as, overhead hoist transports, automated guided vehicles, rail guided vehicles or operators. Hence the bandwidth (i.e. capacity and rate) of the automated material handling system becomes a factor effecting the through put of a workstation system in the fabrication facility, and consequently effecting the through put of the whole facility. For example, in order for substrates to be transferred in conventional systems the substrates are placed in cassettes by a particular workstation and removed from the front end loader of the particular workstation system and placed on the related transport for delivery to the next workstation system. This creates increased risk of contamination and significantly lost time.
High throughput transport devices designed to move a substrate or workpiece between remote locations within areas having a limited footprint are in high demand. The desire to move a workpiece from one position to the next, involves not only a high throughput rate, but also repeatable accurate placement of workpieces registered in a predetermined orientation on a supporting surface.
The exemplary embodiments described below incorporating features of the invention provide a means for bypassing the cassette or other automated transport system when it is desired to sequentially process substrates in processing chambers of adjacent workstation systems thereby increasing throughput compared to conventional systems as will be further described. Further, the exemplary embodiments incorporate alignment and metrology measurement functions as part of the bypass transfer for further increases in throughput without affecting footprint constraints.